The United States and Canada generate about 100,000,000 pounds of spent base-metal catalyst per year, about half of which is spent hydroprocessing catalysts. The present invention relates to a process for regenerating spent heavy hydrocarbon hydroprocessing catalysts. More specifically, the present invention relates to a process for regenerating spent heavy hydrocarbon hydroprocessing catalysts that have been deactivated with coke and metal deactivants such as nickel and vanadium.
With respect to the present invention, the term hydroprocessing is used to refer to a process for hydrodemetallation, hydrodesulfurization, hydrodenitrogenation, and hydroconversion wherein the term hydroconversion encompasses the hydrocracking and hydrotreating of hydrocarbon streams containing asphaltenes and contaminant metals. Hydroprocessing catalysts used to treat heavy hydrocarbon streams, such as resids, are deactivated as a result of metals deposition and coke deposition. These deposition materials modify the rate of reaction as well as accelerate the rate of catalyst deactivation. The various metal deposits tend to occlude catalyst pores and poison the hydroprocessing catalyst, while coke deposits similarly reduce pore size and surface area of the hydroprocessing catalyst.
Typically, hydroprocessing catalysts possess substantial macropore volume in order to effect metals removal from the heavy hydrocarbon feed streams. Heavy hydrocarbon hydroprocessing catalysts possess the capacity to adsorb contaminant metals, such as nickel and vanadium, in an amount ranging up to about 100 wt.% of the fresh catalyst weight. However, due to the rapid coke deposition rate, the catalyst is deactivated prior to achieving its full metals adsorption capacity. Such catalysts are taken out of service when they contain as little as 10 wt.% nickel plus vanadium. If the spent catalyst is not regenerated, it is subsequently sent to a metals reclamation facility where the proceeds therefrom, in part, depend upon the vanadium content of the spent catalyst.
Thus, the prior art is replete with processes suitable for regenerating or rejuvenating such hydroprocessing catalysts. In general, these processes involve removing the deposited contaminant metals, preceded or followed by a coke burn-off step. The metals can be removed first, for example, by acid-leaching with oxalic acid or sulfuric acid, followed by the decoking step. While some processes afford the extraction of nickel and vanadium without removing active metals [U.S. Pat. No. 4,677,085 (Nevitt)], catalytic metals such as cobalt and molybdenum may have to be reimpregnated (Silbernagel, B. G., R. R. Mohan, and G. H. Singhal, "NMR Studies of Metal Deposition on Hydroprocessing Catalysts and Removal with Heteropolyacids," ACS Div. Ind. Eng. Chem. Catal. Mater. Relationship Struct. Reactivity Symposium (San Francisco 6/13-16/83) ACS Symp. Ser. 248, 91 (1984)).
In the fluidized catalytic cracking (FCC) art, feedstocks containing vanadium are handled by the use of passivation agents. For instance, U.S. Pat. No. 4,451,355 (Mitchell et al.) discloses the use of calcium, antimony, tin, barium, manganese, and bismuth additives to mitigate the poisonous effects of nickel, vanadium and iron contained in FCC feedstocks. U.S. Pat. No. 4,364,847 (Tu) discloses the use of lithium to carry out the subject pacification.
Similarly, U.S. Pat. No. 4,549,958 (Beck et al.) discloses treatment of hydrocarbon oil having a significant content of vanadium. A fluidizable sorbent is used to demetallize and decarbonize the hydrocarbon oil. The sorbent contains additive metal components in an amount sufficient to complex with and immobilize the flow characteristics of sodium vanadates or vanadium pentoxide formed during the sorbent oxidative regeneration step. These additive metals are selected from the group consisting of Mg, Ca, Ba, Sc, Y, La, Ti, Zr, Hf, B, Ta, Mn, In, Te, an element in the lanthanide or actinide series, or an organo-metallic compound of the additive metal component.
As mentioned above, the metals, especially vanadium, tend to deactivate hydroprocessing catalysts; however, these metals also tend to affect the catalyst's physical properties, such as the crush strength and the attrition rate of a regenerated hydroprocessing catalyst. Further, most regeneration processes achieve only partial or mixed restoration of fresh activities regardless of whether the contaminant metals are removed. In this connection, the paper "Studies of Poisoning and Regeneration of Hydrodesulfurization and Hydrodemetallization Catalyst during Treatment of Venezuelan Crude Oils" J. Japan Petrol. Inst. 22,(4), 234-242 (1979) shows that where catalysts have been used in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) processes to treat Venezuelan feeds, the activity loss could only be regenerated by about 70 to 90 percent because vanadium deposits modified the activity strongly by blocking catalyst pores and active centers.
In ACS Div. of Petroleum Preprints Vol.27 No.3 679-81 (Sept. 1982), a process is disclosed wherein a commercial Al-Co-Mo catalyst is regenerated using a solvent-extraction treatment to extract contaminant metals with organic reagents capable of forming water-soluble metal complexes. The extraction step was followed by a coke burning step. The regenerated catalyst possessed a lower hydrodesulfurization activity yet a higher hydrodevanadization activity.
U.S. Pat. No. 4,795,726 (Schaper et al.) discloses a method for regenerating spent alumina-based catalysts that have been employed in treating metals-contaminated hydrocarbon feedstocks. The subject process involves a steam treatment step, coke burn-off step, and a basic medium treatment step. The process may require the addition of catalytic metals to the regenerated catalyst since the catalytic metals are removed together with the vanadium and nickel.
In a paper, Ernst W. R., et al. "GTRC Process For Removing Inorganic Impurities From Spent Hydrodesulfurization Catalysts" Minerals and Metallurgical Processing, 4 (2), 78 (1987), a method is disclosed for removing nickel and vanadium contaminants from spent hydrodesulfurization catalysts that involves pretreating the catalyst with H.sub.2 S followed by the extraction of nickel and vanadium with an acidic solution of ferric ion. The subject method results in the removal of some catalytic metals, such as 50 percent of the cobalt and 5 percent of the molybdenum. The regenerated catalyst possessed hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of about 70 percent of the fresh catalyst activities, while the deactivation rates, for HDS but not HDN of the regenerated catalyst were superior to those of the fresh. The regenerated catalyst possessed superior hydrodemetallation activity.
Various additives or reagents have been employed to assist in the regeneration of hydroprocessing or hydrorefining catalysts. For instance, U.S. Pat. No. 4,581,129 (Miller et al.) discloses a process for regenerating a hydrorefining catalyst which results in restoration of catalytic activity, no loss in the strength of the support material, and no unacceptable loss of active metals. The subject patent discloses an embodiment of the invention wherein a mild heat treatment or a partial decoking step is preceded or immediately followed by an extraction of the vanadium and nickel metal contaminants with an acidic solution. A preferred metals-extraction method is disclosed in U.S. Pat. No. 4,089,806 (Farrell et al.) wherein oxalic acid or in one or more water-soluble, nitrate-containing compounds, such as nitric acid, and water-soluble inorganic nitric salts are used. The subject regeneration process involves incorporating a phosphorous component after the partial decoking and extraction step prior to combusting essentially the remainder of the coke from the catalyst.
The subject patent offers the explanation that carrying out the decoking in the absence of phosphorous by combustion releases SO.sub.2 from the sulfur on the catalyst, which SO.sub.2, in the presence of O.sub.2, and the large quantities of vanadium contaminants on the catalyst, are partially converted to SO.sub.3. During combustion, the SO.sub.3 reacts with the alumina component of the hydrorefining catalyst to form aluminum sulfate, and, as a result, the crushing strength, pore volume, surface area, and activity of the catalyst are often reduced. The subject patent further explains that vanadium on the deactivated catalyst is initially in the +3 or +4 oxidation state in such forms as V.sub.2 S.sub.3 or VS.sub.2. Thus, when a sufficient temperature threshold is surpassed, the vanadium is converted to the +5 oxidation state suitable for promoting the SO.sub.2 conversion to SO.sub.3. Incorporation of phosphorous components with the deactivated catalyst is thought to passivate or inhibit, by some chemical reaction mechanism, the vanadium conversion to the +5 oxidation state and thereby inhibit the sulfation mechanism.
The Patentees also point that their metals-extraction process may result in a reduction of MoO.sub.3 and CoO catalytic components, e.g., from 12 and 4 wt.% to 8 and 3 wt.%, respectively. Thus, Patentees suggest in a highly preferred embodiment of their invention, that catalytic components be reintroduced to the rejuvenated catalyst. Patentees also suggest that the rejuvenated catalyst be crushed and reformulated into particulate form by extruding a mixture of a gel and the crushed rejuvenated catalyst.
U.S. Pat. No. 4,089,806 (Farrell et al.) as mentioned above also discloses a process for removing vanadium and nickel deactivants from contaminated hydrodesulfurization catalysts comprising Group VIB and/or Group VIII active components on refractory oxide supports. In this process, the spent catalyst is contacted with an aqueous regenerant solution comprising oxalic acid and one or more soluble nitrate-containing compounds from the class consisting of nitric acid and water-soluble inorganic nitrate salts. Suitable nitrate salts include sodium nitrate, ammonium nitrate, potassium nitrate, calcium nitrate, magnesium nitrate, copper nitrate, etc., with the preferred salt being aluminum nitrate. This contacting results in the removal of vanadium and nickel contaminants from the surface of the deactivated catalyst and substantially rejuvenates the catalyst for hydrodesulfurization purposes, provided that such removal is accomplished prior to the burning off of any coke present in the catalyst.
The patent further maintains that subsequent decoking after the contacting treatment with the regeneration solution is optional. Sufficient activity is restored by the method described without decoking being necessary. Patentees maintain that decoking of heavily deactivated catalyst may actually result in a loss of some of the activity restored by the treatment with the regenerant solution. Patentees further maintain that it is a critical aspect of the invention that the deactivated catalyst should not be decoked prior to treatment with regenerant solution, primarily because such decoking is generally counterproductive. Decoking by combustion prior to the treatment described herein releases SO.sub.2 from the sulfur in the coke which, in the presence of O.sub.2 and large quantities of vanadium, deactivates the catalyst. The so-produced SO.sub.3 then reacts with the alumina catalyst support to form aluminum sulfate, thereby lowering the crush strength.
Farrell et al. maintain that the rejuvenated catalyst will have at least 30 percent, usually 70 percent and an occasion over 80 percent of the fresh original activity. Patentees explain that full restoration is generally not possible since 10 percent or less of the active catalytic components are removed from the catalyst during the regeneration process.
U.S. Pat. No. 4,268,415 (Mohan et al.) discloses a process for the regeneration of spent hydrodesulfurization catalysts with heteropoly acids and hydrogen peroxide. In particular, the patent discloses a process wherein a spent hydrofining catalyst is regenerated by contacting the spent catalyst with a solution of a heteropoly acid having the general formula of H.sub.x (YM.sub.12 O.sub.40) where Y is at least one element selected from the group consisting of phosphorus, silicon, titanium, germanium, arsenic, zirconium, thorium and cerium, M is at least one element selected from the group consisting of molybdenum, tungsten, niobium and tantalum and x is 3 when Y is pentavalent (P, As) and x is 4 when Y is tetravalent (Si, Ti, Ge, Zr, Ce, Th). The heteroploy acid solution preferably contains 1 to 50 wt.% hydrogen peroxide. Patentees maintain that the method results in the extraction of about 70 to 100% vanadium and about 90% nickel and about 50% cobalt with essentially no loss of molybdenum and aluminum coupled with the preservation of the structural integrity of the catalyst support. The spent catalyst regeneration process can also further include additional processing by doping the demetallized catalyst with cobalt followed by calcination. The subject cobalt impregnation improves or promotes carbon decoking, further sulfur removal, and an additional increase in surface area and pore volume. Patentees maintain that hydrorefining activity and product selectivity of the regenerated spent catalyst is substantially the same as that of the fresh catalyst.
U.S. Pat. No. 4,728,417 (Aldag, Jr. et al.) discloses a process wherein an additive comprising a mixture of at least one decomposable molybdenum compound selected from the group consisting of molybedenum dithiophosphates and molybdenum dithiocarbamates and at least one decomposable nickel compound selected from the group consisting of nickel dithiophosphates and nickel dithiocarbamates is mixed with the hydrocarbon feed. The hydrocarbon feed containing the additive is then contacted with the hydrofining catalyst. The additive can be added when the catalyst is new, partially deactivated or spent with a beneficial result occurring in each case. Patentees maintain that the introduction of the additives slows down the catalyst rate of decline from the time of introduction and in some cases improves at least a partially spent or deactivated catalyst from the time of introduction.
Accordingly, the prior art presents a dilemma in that contaminant metals must be removed to retain or restore physical and catalytic properties of the spent hydroprocessing catalyst, yet its reclamation value is diminished when the metal, i.e., vanadium, content of the spent catalyst is reduced. Thus, there is a need for a catalyst regeneration process wherein the catalyst poisoning contaminant metals, such as vanadium, need not be removed such that the demetallization capacity of the hydroprocessing catalyst is entirely utilized thereby increasing its eventual reclamation value. Further, there is a need for a regeneration process that restores all catalytic activities without the need to reimpregnate catalytic metals while concomitantly maintaining requisite physical properties such as attrition resistance, attrition resistance being an especially important property when the catalyst is employed in an ebullated bed reactor system.
It has now been discovered that when a Group VIB metal component is incorporated into the spent catalyst in accordance with the present invention, catalyst activities can be restored with no need for removal of contaminant metals coupled with no loss in catalyst attrition resistance.